1. Field of the Invention
The present invention is directed to a method for synthesizing dihydro-1,4-dithiins. More specifically, the present invention is directed to a method for forming dihydro-1,4-dithiins by the reaction of an acyloin or a halocarbonyl compound with an organic thiosulfate.
2. Background Of The Prior Art
Compounds of the general class, dihydro-1,4-dithiins have several important uses. U.S. Pat. No. 3,997,323 discloses the use of these dithiins as herbicides. They have also been reported as useful as plant-growth regulants (U.S. Pat. No. 3,920,438.) In U.S. Pat. No. 4,004,018, dihydro-1,4-dithiins compounds are recited to have utility as fungicides and bactericides. A related use, as viricides, is disclosed in U.S. Pat. No. 4,097,580.
The prior art suggests several methods for synthesizing this important class of compounds. One such method is reported in U.S. Pat. No. 4,026,906. The method suggested by the '906 patent comprises the reaction of a halocarbonyl compound with a 1,2-dithiol. A somewhat similar method [Massingill, J. Org. Chem. 35, 823 (1970)] is the reaction of a ketone with a 1,2-dithiol followed by halogenation and ring expansion to a dithiin. A modification of these reactions is disclosed in the above mentioned U.S. Pat. No. 4,026,906, the reaction of the 1,2-dithiol with an alpha-halo-beta-keto-ester. Alternatively, the same '906 patent discloses the reaction of a 1,2-dithiol with a beta-keto-ester followed by ring expansion. In the last two of these syntheses, the first reactive step is followed by decarboxylation. A further method of forming dihydro-1,4-dithiin compounds is disclosed in U.S. Pat. No. 3,755,362. In the '362 patent formation of these dithiins results from the reaction of a mercaptoketone with a thirane. Finally, a still further method of obtaining these important compounds is disclosed in co-pending U.S. patent application, Ser. No. 247,670, filed Mar. 26, 1981, of Tsai et al, now U.S. Pat. No. 4,319,033, in which a dithiol is reacted with acyloin.
Each of the above recited methods of synthesis of dihydro-1,4-dithiin compounds involves the formation and isolation of unpleasant and undesirable intermediates. 1,2-Dithiol compounds, a class of compounds employed in several of the methods mentioned above, have a penetrating, persistent and nauseating odor, even in low concentrations. Mercapto ketones and thiranes are similarly characterized by their vile odor. Furthermore, these compounds are undesirable in that they are chemically unstable and require special handling techniques. Even more important than these esthetically unpleasant characteristics of the reactants employed in the prior art is the fact that expensive apparatus, designed to contain odors, protect workers and abate pollution, is required in all of the above methods for making dihydro-1,4-dithiins.